1. Field of the Invention
The present invention relates to an air compressor for generating compressed air used in a pneumatic tool such as a pneumatic nailing machine, and a method for controlling the air compressor.
2. Background Art
Generally, an air compressor used for pneumatic tool is configured so that a crankshaft of a compressor body is driven to rotate by a motor to reciprocate a piston in a cylinder in accordance with the rotation of the crankshaft to thereby compress air sucked in from an inlet valve. The compressed air generated in the compressor body is discharged from an outlet valve to an air tank through a pipe and reserved in the tank. The pneumatic tool does its work such as nailing by using the compressed air reserved in the tank.
The air compressor is often carried to a building site and used outdoors or is often used in a densely populated place. For this reason, the air compressor needs to be improved from various viewpoints. According to the present inventors' investigation into how the air compressor is actually used on the work site, users' demands and technical problems can be collected into the following items.
(1) Reduction of Noise
Because the air compressor has a mechanism for converting the rotation of the motor into the reciprocating motion of the piston in the cylinder, it is unavoidable that considerable noise is produced when the motor is rotating. Furthermore, because the pneumatic tool such as a nailing machine using compressed air generated by the air compressor produces operating noise when the pneumatic tool is operating, the operating noise is combined with the air compressor's own noise so that considerable noise is produced around the building site. Particularly when the air compressor is used in the early morning or after the evening in a densely populated place, there is a strong demand that the noise should be as low as possible.
(2) Improvement in Power and Efficiency
The place where the air compressor is used is not always in a sufficient electric power environment. The air compressor may be rather used in such an environment that it is impossible to keep a sufficiently high voltage because a long cord needs to be used for providing a power-supply voltage from another place, or in such an environment that a great deal of compressed air must be consumed because a large number of pneumatic tools need to be used simultaneously.
For this reason, it may be impossible to produce a high-power output from the air compressor. If, for example, a nailing machine is used in the condition that the output is insufficient, nailing is performed shallowly and there arises a problem that it is impossible to nail a workpiece sufficiently.
Generally, 26 kg/cm2 to 30 kg/cm2 of air are reserved in the air tank of the air compressor. It is unavoidable that the air leaks little by little when there is no tool used. There is another problem that lowering of efficiency may be brought about in accordance with how to use the air compressor.
(3) Improvement in Size Reduction and Portability
It is rare that the air compressor for pneumatic tool is used as a stationary type compressor. In most cases, the air compressor is of a portable type, so that the air compressor is used after carried to a building site. Therefore, the air compressor needs to be as small in size as possible and as excellent in portability as possible. Accordingly, complicating the configuration of the compressed air generation portion and the drive portion for driving the compressed air generation portion must be avoided to the utmost in order not to spoil portability.
(4) Prolongation of Life
There is a problem that the life of the air compressor used for pneumatic tool is shorter than the life of a compressor used for refrigerator, air-conditioner, etc. Although it is unavoidable in one aspect that the air compressor is short-lived because the air compressor is used in a harsh environment, suppression of change in load to the utmost or suppression of generation of wasteful compressed air to the utmost is required for attaining prolongation of the life.
(5) Suppression of Increase in Temperature
It is unavoidable that the temperature of the air compressor becomes considerably high because of the reciprocating motion of the piston in the cylinder and the electric current flowing in the motor for driving the piston. The high temperature of the air compressor, however, causes increase in loss and disturbance of efficiency. Therefore, suppression of increase in temperature of the air compressor to the utmost is required eagerly.